Coma: Causes, diagnosis, treatment, and outlook

A coma is a deep state of unconsciousness. It can happen as a result of a traumatic accident, such as a blow to the head, or a medical condition, for example, some types of infection.

Coma is different from sleep because the person is unable to wake up.

It is not the same as brain death. The person is alive, but they cannot respond in the normal way to their environment.

Whether or not they are conscious, or how many people are conscious during a coma, or the level of consciousness, is a question that scientists are currently investigating.

Levels of consciousness and responsiveness will depend on how much of the brain is functioning. A coma often lasts for a few days or weeks. Rarely, it can last for several years.

If a person enters a coma, this is a medical emergency. Rapid action may be needed to preserve life and brain function.

Fact facts on coma

During a coma, a person does not react to external stimuli and they will not show normal reflex responses.

Comatose patients do not have sleep-wake cycles.

Reasons for a coma include intoxication, nervous system disease, metabolic disease, infections, or a stroke.

Depending on the cause and the extent of damage, a coma can occur rapidly or gradually, and it can last from several days to several years, though most last from days to weeks.

What is a coma?

A coma
A coma is a state of deep unconsciousness.

A person who is experiencing a coma cannot be awakened, and they do not react to the surrounding environment. They do not respond to pain, light, or sound in the usual way, and they do not make voluntary actions.

Although they do not wake up, their body follows normal sleep patterns. Automatic functions, such as breathing and circulation, normally continue to function, but the person’s thinking ability is suppressed.

According to the National Institutes of Neurological Disorders and Stroke (NINDS), the person may sometimes grimace, laugh, or cry as a reflex.

Coma may occur for various reasons, such as intoxication, a disease or infection that affects the central nervous system (CNS), a serious injury, and hypoxia, or oxygen deprivation.

Sometimes, a doctor will induce a coma using medications, for example, to protect the patient from intense pain during a healing process, or to preserve higher brain function following another form of brain trauma.

A coma does not usually last for more than a few weeks. If the patient’s condition does not change after an extended period, it may be reclassified as a persistent vegetative state.

If a persistent vegetative state lasts for months, the person is unlikely to wake up.


During a coma, a person cannot communicate, so diagnosis is through the outward signs.

These include:

closed eyes

limbs that do not respond or voluntarily move, except for reflex movements

lack of response to painful stimuli, except for reflex movements

How long these will take to develop, and how long they will continue, depend on the underlying cause.

Before entering a coma, a person with worsening hypoglycemia (low blood sugar), or hypercapnia (higher blood CO2 levels), for example, will first experience mild agitation. Without treatment, their ability to think clearly will gradually decrease. Finally, they will lose consciousness.

If a coma results from a severe injury to the brain or a subarachnoid hemorrhage, symptoms may appear suddenly.

Anyone who is with the person should try to remember what occurred just before the coma started, because this information will help determine the underlying cause and give a better idea of what treatment to apply.

Recognizing symptoms

A first responder may start by using the AVPU scale, try to gauge the level of consciousness.

The AVPU scale looks at the following areas:

Alertness: How alert is the person?

Vocal stimuli: Do they respond to another person’s voice?

Painful stimuli: Do they respond to pain?

Unconscious: Are they conscious?

Alert is the most conscious state, and unconscious is the least. This helps the health professional assess whether this is likely to be an emergency. If the person is alert, there is no risk of coma.

In the hospital, doctors may apply the Glasgow coma scale (GCS) to assess the person’s condition in more detail.

Patients with deep unconsciousness may be at risk of asphyxiation. They may need medical help to secure the airways and ensure they continue to breathe. This could be a tube that passes through the nose or mouth, into the lungs.

Can a person hear and think when they are in a coma?

doctor holds woman's hand
A person in a coma may benefit from sensory stimulation, such as holding a hand.

There is some evidence that people can hear and understand spoken instructions during a coma.

In 2011, neuroscientists using fMRI scanning technology observed brain activity in a man who had been in a coma for 12 years after a road traffic accident.

For example, when they asked the man to imagine he was playing tennis or walking round his house, his brain activity reflected that he was thinking of doing these things.

Scientists now believe that 15 to 20 percent of people in a so-called vegetative state may be fully conscious. Advances in technology mean that we are better able to understand what people are experiencing during a coma.

A person who is visiting a friend or family member who is in a coma can speak to them as they normally would, for example, explaining what has been happening during the day. It is unclear how much they can understand, but there is a chance the person may be able to hear and understand. They may like to listen to music.

Research has also suggested that stimulating the senses of touch, smell, sound, and vision may help the person recover. A visitor could help by wearing a favorite perfume or holding the person’s hand.

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Causes or a coma vary, but they all involve some level of injury to the brain or CNS.

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